Do no harm: stem cells created without destroying healthy embryos.
Unlike any cell known in adults, embryonic stem cells can morph into virtually any of the body's cell types, such as nerve, muscle, or heart. Many researchers have proposed exploiting this unique capability to make new cells for the treatment of injuries or diseases such as Parkinson's disease (SN: 4/2/05, p. 218). However, to isolate a new line of embryonic stem cells, scientists have had to first destroy an early embryo.
"Many people, including the President, are concerned about destroying life in order to save life," says Robert Lanza of Advanced Cell Technology in Worcester, Mass.
Seeking to resolve this dilemma, Lanza and his colleagues looked to a technique commonly used to diagnose genetic diseases in embryos. Known as pre-implantation genetic diagnosis, the procedure removes one cell from an eight-cell-stage embryo and examines its DNA for defects. The remaining seven-cell embryo, after being implanted in the mother's womb, can develop into a normal baby.
Lanza and his colleagues started their new work by performing a similar procedure on eight-cell mouse embryos. However, rather than subjecting the removed cells to genetic testing, the researchers placed them in lab dishes with proteins that encouraged the cells to divide.
The researchers added to the mix some previously obtained mouse embryonic stem cells, which secreted chemical signals that the team says coaxed the newly isolated cells to become stem cells. When supplied with various growth factors, the new cells morphed into a variety of cell types.
Alexander Meissner and Rudolph Jaenisch of the Whitehead Institute for Biomedical Research in Cambridge, Mass., used a different approach in their attempt to alleviate ethical concerns. Earlier research had shown that a gene known as cdx2 is pivotal in creating tissues that an embryo needs if it's to implant in the womb.
Jaenisch and Meissner inactivated cdx2 in mouse skin cells. Then, the researchers removed the nuclei from these skin cells and transplanted them into unfertilized eggs that had had their own nuclei removed. A chemical treatment prompted the eggs to divide.
Without active cdx2, the resulting balls of cells couldn't implant in surrogate mouse mothers. However, they did produce all types of cells in the body except intestinal cells, which need cdx2 to develop normally. When the researchers put the embryonic cells into mice and reactivated the gene, the cells formed healthy intestines.
Both studies appear in an upcoming Nature.
Although these methods may ease ethical concerns for some people, others may view them as just "a new version of embryo destruction," says Alta Charo, a bioethicist at the University of Wisconsin-Madison. She notes that research hasn't ruled out the possibility that a single cell plucked from an early embryo, as in Lanza's work, can form a new embryo. Furthermore, some people may view the abnormal clumps of cells missing cdx2 in the Meissner Jaenisch study as "terminally ill" embryos rather than just masses of cells.
Irving Weissman of Stanford University School of Medicine agrees that many people won't be convinced that the new techniques don't destroy embryos. However, he adds, "if even a small number of researchers can enter the field with this new technology, somebody's life might be saved."
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|Title Annotation:||This Week|
|Date:||Oct 22, 2005|
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